Magnetron



Jan. 25, I 1949. J. 'P. BLEwEfT ET AL MAGNETRON Filed Sept. 23, 1944 Inventors .m u tm m e n m W 0 nldm p A n .w h? e wm CW P Patented Jan. 25, 1949 MAGNETRON John P. Blewett and Robert V. Langmuir, Schenectady, N. Y., assignors to General Electric Company, a corporation of New York Application September 23, 1944, Serial No. 555,496

1 Claim. 1

Our invention relates to electric discharge de- Vices and more particularly to improved electric discharge devices of the magnetron type.

Numerous magnetron constructions employing an array of anode elements about a centrally located cathode have been employed as high frequency oscillation generators. In the operation of devices of this character, the electrons in the interelectrode space are subjected to the action of mutually perpendicular electric and magnetic fields which cause the electrons to move in curvilinear paths and to excite the anode structure at its resonant frequency. Devices of the character described above have in the past been characterized by a limited power output. In accordance with the teachings or our invention we provide an improved magnetron and particularly an improved cathode construction and mounting which is particularly well adapted for magnetrons of high power output.

It is an object of our invention to provide a new and improved electric discharge device of the magnetron type.

It is another object of our invention to provide a new and improved cathode construction particularly adapted for use in electric discharge devices of the magnetron type.

It is still another object of our invention to provide a new and improved mounting and fluid cooling arrangement for the cathode of an electric discharge device.

In the illustrated embodiment of our invention a pair of anode elements are mounted within a cylindrical envelope with the anode faces defining a cylindrical space which is coaxial with the envelope. A cathode in the form of a cylindrical body, having at least the major surface portion thereof formed of material which is a good secondary emitter, is supported in the cylindrical space defined by the anode members by an elongated hollow conducting sleeve which is supported from and in insulated-relation with respect to the cover-or end of the envelope. The cathode body is provided with a recess Within which a thermionic cathode member is supported to provide a source of primary electrons. The lead-in conductor for the thermionic cathode is brought out to the cathode support through aseparate tubular member which is hermetically sealed. Conduits for conducting cooling fluid to and from passages formed within the cathode body are also sup ported within the hollow cathode support.

For a better understanding of our invention reference may behad to the following description 3 is a perspective view, partially broken away, of a cathode body construction in accordance with our invention.

Referring now to Fig. 1 of the drawing, we have shown our invention embodied in a magnetron device including a generally cylindrical envelope 1 preferably formed of good conducting material such as copper. The envelope encloses an anode structure comprising two anode members 2 and 3 having semi-cylindrical faces arranged in opposed relation to provide a circular array. As illustrated most clearly in Fig. 2, the members 2 and 3 are mounted in mutually spaced relation to provide gaps 4 and 5 between them and with the cylindrical space defined by the anode members coaxial with the envelope l. The anode member 2 is supported within the envelope by a pair of hollow tubular members 5 and l which extend through the side wall of the envelope 2 in a direction generally parallel to the gaps 4 and 5. In a similar manner, the anode member 3 is supported by the hollow tubular members 8 and 9. These tubular members 6-9, inclusive, may be formed of copper tubing and are hermetically sealed to the wall of the envelope. The ends of the tubes extending to the exterior of the envelope provide for connections with a system for circulating fluid through the tubular members and the interior of the anode members 2 and 3.

An elongated cylindrical cathode body ii] is supported centrally in the cylindrical space defined by the anode members 2 and 3 by means of a tubular member H which extends in alinement with the cathode body and is supported from a sleeve 12 by cooperating parts on tube H and sleeve l2 which are secured together by means of a threaded cap iii. The sleeve i2 is supported from the cover I l of the envelope by means of a cylindrical glass sleeve [5 having one end sealed,

to the lower edge of the sleeve l2 and the other end sealed to the upper edge of an upstanding flange l6 which may to advantage be formed integral with the cover it. The cathode body I i3 is formed of material which is a good secondary emitter as copper-beryllium or, as'illustrated in the drawing, it may be formed of a conducting material such as copper coated with a layer of magnesium I! or a compound which is predominately magnesium. This material may be applied in a thin layer by the Schoop process. As illustrated in Fig. 3, the cathode body is provided with a pair of passages l3 and IS extending lengthwise of the cathode body and joined at the lower end by a transversepassag 25. These passages are enlarged at the upper end of the cathode body to receive conduits 2i and 22 which extend upwardly through the supporting sleeve II and extend from an opening centrally located in the cap I3.

A source of primary electrons in the interelectrode space of the device is provided by means of a thermionic cathode 23 which, as illustrated, is in the formof a'filament located in an "axially extending access 2 3 formed in the surface of the cathode body. The recess is deep enough so that the outer edges of tie cathode 23 do not extend beyond the walls defining the recess. The thermionic cathode 23 is preferably supported sothat it may be removed from the discharge device as a sub-assembly. To this end an enclosingtube 25 is joined to the end of the cathode bodysurrounding an opening comnuinicating with the recess 24. This member s hermetically sealed "to the cathode and extends through the sleeve '11 and the central openingin the cap 53. member oi aller diameter thanmember 25 is-positioned within member 25 and has theupper end thereof sealed to the member '25 by a body of vitreous material. 2? such as glass. One end-of the thermionic cathode .is conductively connected with the tubular member Zilandthe other endlll of cathode i "pported in insulated re lation with respect '0 tubularmembey ZB'by the seal .21 and a pl'lnacty of insulating spacers 29. She cathode body is provided with flanges 353 and which are located on opposite sides of the anodemembers 2 an 3 when the cathode is assembled. These flanges serve to confine the electrons in the interelectrode space.

As is well understood by nose skilled in :the art, anode members 2 and 3 together withthe tubular supporting members 3-5, inclusive, and the envelope i provide a resonant structure having a natural frequency, or frequencies, dependupcn the geometry of the VQECd-S parts. In order to control the frequency of the oscillations of'the generator, a tin ng element in theforrn of a movable shorting number '5 provided to vary the effective length of the con ing members 5 and 8. Themember is a able Icy-operation of a thumbscrew support d from the exterior of the envelope by a housing 3 and operating through a Sylphon bellows 35. Highfrequency power may be derived from the resonant structure, including anode members 2 andLS, by a conductor 35 conductively connected with one of the tubular members such as G. .This output conductor may to advantage form the central conductor of a concentric transmission line .the outer conductor 33 01' which is shown as joined to the wall of the envelope 2. Conductors 3.6 and 38 aremaintained in spaced insulated relation by insulating disks 39.

A magnetic field inthe interelectrode spacein a direction generally parallel to the axis of the cathode is provided by pole faces 40 and ii. In accordance with established practice, the pole faces may be part .of a permanentmagnetor a portion of a core structure of an edectrornagnet. In the operation of the illustrated embodiment of our invention electrons emitted from the primary source, the thermionic cathode 23, move in curvilinear paths in the interelectrodespa'ce due to tlie'resultant action of the mutually perpendicular electric and magnetic fields. The elec- 't-ric field is established by unidirectional voltage impressed between the anode structure and 'cathode, and the magnetic field is provided by the pole faces 3% and 3?. A certain number oi -these electrons return to the cathode after traveling circumferentially around the cathode with suffioient elocity to liberate a large number of secondary electrons, thus providing ample electrons $01 the rotating space charge Of'the device. In

A tubular j :of,=the gaps -4 or .5 by substantially 45.

4 assembling the cathode within the magnetron device it is necessary to locate the thermionic cathodewithirespect tothe'gaps4 and 5 so that zthethermionic cathodereceives a-minimum number of returning electrons. If the electron mo- ;tion is in a clockwise direction, as viewed in Fig.

the assembly of the cathode structure and the direction of the magnetic field must be correlated.

.From the preceding description it ,is apparent that wehave provided an improved construction which is rugged, easily assembled and capable of high power continuous wave operation. The thermionic cathode element, which is the .only operative element in the device which might readily be damaged is shielded from the action of the returning .electronsand is formed as .part of a sub-assembly which is readily removed. The water cooling of the cathode limits thetemperature rise due to the back heating of the cathode and permits the high power operation.

While we have shown and described a particular embodiment of our invention, .it will .be obvious to those skilled in the art thatchanges and modifications may be made without departing from our invention in its broader aspects, and we. therefore, aim in the appended claim to cover all such changes and modificationscs fall within the true spirit and scope of our invention.

What we claim new and desireto secure by Letters Patent of the United States, is:

A magnetron discharge device including a cylindrical cathode structure and an annular anode structure coaxially surrounding the oathode structure and comprising spaced anodes defining interaction gaps on diametricallyopposlte sides of said cathode structure, said cathode structure comprising a cylindrical body'having a cylindrical surface of .material which is a good secondary emitter, said body having an axially extending recess directed inwardly from the surface thereof and a thermionic cathode supported in said recess so that said thermionic'cath'ode is shielded from electrons returning to said body from the space charge between said anode and said cathode structures, said recess being located in advance of one-of said gaps'as measured by the direction of rotation of electrons in the space between sald anode and cathode structures by an angular distance less than'half the angular distance' between said gap.

w; JOHN P. BLEWETT. ROBERT V. LANGMUIR.

"REFERENCES CITE!) The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,712,402 Robinson May 7,1929 1,727,373 Macksoud Sept. 10, 1929 1,75'71233 "Bol May 6, 1930 1,881,910 Parker *Oc'tf-ll, 1932 2,130,510 Samuel Sept. 20, 1938 2,295,396 George Sept. 8, 1942 2,469,038 Hansell Oct. '8, 1946 2,411,299 Sloan *Nov.19,1946 

